Frost dates for Mount Ayr, IA
At Mount Ayr, the median last spring frost (32°F) is Apr 25 and the median first fall frost is Oct 12, for a typical growing season of 169 days. For a 90% chance that the last frost has passed, wait until May 9. Nearby ZIP codes are in USDA hardiness zone 5b.
- Apr 25Last spring frost (median)50% chance of 32°F after this date
- May 9Safer planting date10% chance of 32°F after this date
- Oct 12First fall frost (median)50% chance of 32°F by this date
- 169 daysGrowing season (median)between 32°F freezes
Last spring frost dates
The chance that the temperature drops to the threshold after each date.
| Temperature | 90% chance later | 50% chance later | 10% chance later |
|---|---|---|---|
| 36°F | Apr 21 | May 4 | May 20 |
| 32°F | Apr 10 | Apr 25 | May 9 |
| 28°F | Apr 1 | Apr 14 | Apr 29 |
| 24°F | Mar 20 | Apr 6 | Apr 20 |
First fall frost dates
The chance that the temperature has dropped to the threshold by each date.
| Temperature | 10% chance by | 50% chance by | 90% chance by |
|---|---|---|---|
| 36°F | Sep 18 | Oct 1 | Oct 14 |
| 32°F | Sep 27 | Oct 12 | Oct 25 |
| 28°F | Oct 9 | Oct 23 | Nov 3 |
| 24°F | Oct 18 | Nov 1 | Nov 14 |
Growing season length
Days between the last spring and first fall freeze, as the length reached in 9, 5 and 1 out of 10 years.
| Temperature | 9 in 10 years at least | 5 in 10 years at least | 1 in 10 years at least |
|---|---|---|---|
| 36°F | 130 days | 150 days | 168 days |
| 32°F | 149 days | 169 days | 188 days |
| 28°F | 169 days | 191 days | 210 days |
| 24°F | 189 days | 209 days | 228 days |
Chance of a freeze in any year
| Temperature | Chance per year |
|---|---|
| 36°F | 100% |
| 32°F | 100% |
| 28°F | 100% |
| 24°F | 100% |
ZIP codes whose closest station is this one
| ZIP | Hardiness zone | Avg. extreme low | Distance |
|---|---|---|---|
| 50854 | 5b | -15 to -10°F | 4 km |
| 50835 | 5b | -15 to -10°F | 11 km |
| 50860 | 5b | -15 to -10°F | 13 km |
| 50845 | 5b | -15 to -10°F | 15 km |
| 50840 | 5b | -15 to -10°F | 22 km |
Not the official USDA Plant Hardiness Zone Map. Zones shown here are the values published in the USDA-ARS / Oregon State University PRISM Group 2023 ZIP code tables, shown unaltered. For the official interactive map, visit planthardiness.ars.usda.gov.
About this station
- NOAA station ID USC00135769, at 40.7053, -94.2428, elevation 348 m (1,140 ft).
- Data quality: Standard (24+ years of data), 26 years of freeze data.
- Average days per year at or below 32°F: 143.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Beaconsfield (20 km)
- Lamoni (21 km)
- Lamoni (28 km)
- Lamoni Muni Airport (30 km)
- Creston 2 SW (39 km)
- Bedford (41 km)
- Leon 6 ESE (50 km)
- Corning (54 km)
Sources
- NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020, annual/seasonal normals by station (version 1.0.1), file dated June 27, 2023; documentation.
- USDA Agricultural Research Service and PRISM Group, Oregon State University, 2023 Plant Hardiness Zone Map ZIP code tables (CONUS, Alaska, Hawaii, Puerto Rico), files dated November 17, 2023. Data © PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed November 1, 2026. Official map: planthardiness.ars.usda.gov.
- U.S. Census Bureau, 2024 Gazetteer ZIP Code Tabulation Areas file, dated August 30, 2024 (ZIP centroids used to find the nearest station).
Freeze dates are 30-year probabilities, not forecasts. Check your local forecast before planting tender plants.